Cardiac arrhythmia is a condition in which the heart's normal rhythm is disrupted. Certain types of cardiac arrhythmias, including ventricular tachycardia and atrial fibrillation, may be treated by ablation (for example, radiofrequency (RF) ablation, cryoablation, ultrasound ablation, laser ablation, microwave ablation, and the like), either endocardially or epicardially.
Procedures such as pulmonary vein isolation (PVI) are commonly used to treat atrial fibrillation. This procedure generally involves the use of a cryogenic device, such as a catheter, which is positioned at the ostium of a pulmonary vein (PV) such that any blood flow exiting the PV into the left atrium (LA) is completely blocked. Once in position, the cryogenic device may be activated for a sufficient duration to create a desired lesion within myocardial tissue at the PV-LA junction, such as a PV ostium. If a cryoballoon is used as the treatment element of the cryogenic device, the balloon is typically inflated using a fluid coolant, enabling the balloon to create a circumferential lesion about the ostium and/or antrum of the PV to disrupt aberrant electrical signals exiting the PV.
The success of this procedure depends largely on the quality of the lesion(s) created during the procedure. Currently known methods for evaluating lesion quality may include monitoring the temperature within the cryoballoon, but this method can be inaccurate. The success of a PVI procedure also depends on whether the cryoballoon has completely occluded the PV. For example, a complete circumferential lesion is produced only when the cryoballoon has completely occluded the PV. Incomplete occlusion allows blood to flow from the PV being treated, past the cryoballoon, and into the left atrium of the heart. This flow of warm blood may prevent the cryoballoon from reaching temperatures low enough to create permanent lesions in the target tissue, or could leave gaps of non-ablated tissue at regions where blood leaks past the balloon. The creation of reversible lesions may not be sufficient to achieve electrical isolation and, as a result, atrial fibrillation may be likely to reoccur. Additionally, even if the PV is completely occluded, suboptimal operation of the cryoablation system may result in cryoballoon temperatures that are not low enough, or not applied for a sufficient amount of time, to create permanent lesions in the target tissue.
Current methods of assessing or monitoring PV occlusion may include monitoring changes in impedance measurements of blood and tissue. Although these methods may be effective, changes in recorded impedance caused by incomplete PV occlusion may be small and could be difficult to detect when trying to quantify the importance of the blood leak around the balloon. Both blood and tissue conduct electricity well and the distinction between their respective conductivities is small.
It is therefore desirable to provide a cryoablation method, system, and device that allows for real-time and accurate assessment of PV occlusion before a PV ablation procedure based on recorded impedance measurements. It is also desirable to provide for a method, system, and device that allow for the communication of PV occlusion assessment to the operator quickly and easily.